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66 SMT Magazine • August 2017 between the metal parts. The objective is to cre- ate a firm, airtight, corrosion-resistant, electri- cally and thermally conductive interconnec- tion. The solder is mostly designed from alloys in the form of solder wire, solder bar or solder paste. Depending on the scope of application of the final product, these alloys are composed of tin, lead, antimony, silver and/or copper. In the solder, fluxing agents can be contained, which are compiled from different chemical composi- tions such as rosin. Normally, halogen-free flux agents are used to support the build of proper solder joints. Automated Soldering Procedures and Hand Soldering Some decades ago, numerous workers, equipped with soldering irons, soldered electri- cal assemblies by hand, whereas today automat- ed soldering systems of different size are used. These plants are highly specialized systems and perform a unique soldering technique (e.g. re- flow soldering or selective soldering). The use of these systems depends on type and lot size of the assemblies. Many production lines feature different systems, which are used according to their distinct technology. Hand soldering at manual workplaces is still found in the vast majority of assembly produc- tion plants. The main application area is for pre-production runs, prototyping and repair. Released Airborne Pollutants Depending on areas of application of the fin- ished assembly and requirements of the compo- nents, various soldering alloys and flux agents are considered. During the soldering process, large parts of the flux agent and a small por- tion of the solder will evaporate. The emerging aerosols and particles could be released into am- bient air. This will not only spread unpleasant odours, but these airborne pollutants can lead to serious medical conditions. Particularly dan- gerous substances are aldehydes, which emerge from materials containing colophony; some of them may be carcinogenic. In addition, gases are released from coatings, adhesives or sub- strates during heating of the assembly. These gases also transport sticky aerosols, which build up in the soldering machines or— even worse—on the products and contami- nate them. This leads to increased cleaning and maintenance costs, and the operability of the plant can be impaired. In addition, the manu- factured products may even be corroded by the contaminations, which could affect functional- ity and quality. In conventional wave soldering processes, the entire printed circuit board is fluxed. The emerging spray mists from alcohol-based flux and other evaporations may lead to explosive, highly flammable vapor/air mixtures. SOLDERING FUMES IN ELECTRONICS MANUFACTURING Figure 2: PCB during wave soldering process with soldering fumes (Courtesy of SEHO Systems). Figure 3: The threefold damaging effect of solder fumes.